downtime vs time period

downtime and time period both are nouns.

Word	Noun	Adjective	Verb	Adverb
downtime	Yes	No	No	No
time period	Yes	No	No	No

As nouns, time period is a hypernym of downtime; that is, time period is a word with a broader meaning than downtime:

downtime: a period of time when something (as a machine or factory) is not operating (especially as a result of malfunctions)
time period: an amount of time

Other hypernyms of downtime include period, period of time.

downtime (noun)	time period (noun)
a period of time when something (as a machine or factory) is not operating (especially as a result of malfunctions)	an amount of time